Multistate Outbreak Investigation of Salmonella Infections Linked to Kratom: A Focus on Traceback, Laboratory, and Regulatory Activities

Abstract: During spring 2018, the U.S. Food and Drug Administration (FDA), Centers for Disease Control and Prevention, and state and local public health agencies responded to a multistate outbreak of gastrointestinal illnesses caused by multiple Salmonella serovars and associated with consumption of kratom, a product harvested from a tropical tree native to Southeast Asia. The outbreak included 199 case-patients reported by 41 U.S. states, with illness onset dates ranging 11 from January 2017 to 8 May 2018, leading to 54 hospitalizations and no deaths. Case-patients reported purchasing kratom products from physical and online retail points of service (POSs). Products distributed to 16 POSs where 24 case-patients from 17 states purchased kratom were selected for traceback investigation. Traceback revealed that the kratom was imported from several countries, the most common being Indonesia. Local and state officials collected product samples from case-patients and retail POSs. The FDA collected 76 product samples from POSs and distributors, of which 42 (55%) tested positive for Salmonella. The positive samples exhibited a range of pulsed-field gel electrophoresis patterns and whole genome sequence genetic heterogeneity, and 25 (60%) of 42 samples yielded at least one isolate indistinguishable from one or more outbreak-related clinical isolates. Although it does not exclude a possibility of a single contamination source, the extent of genetic diversity exhibited by the Salmonella isolates recovered from product samples and a lack of traceback convergence suggested that kratom was widely contaminated across multiple sites from which it was grown, harvested, and packaged. As a result of the contamination, kratom products were recalled by numerous firms (both voluntarily and mandatory). Epidemiologic, traceback, and laboratory evidence supported the conclusion that kratom products were associated with illnesses.